The pharmacokinetics and pharmacodynamics of muscle relaxant antagonists, e.g., neostigmine, pyridostigmine and edrophonium, may be altered by renal and hepatic dysfunction, in patients undergoing anesthesia and surgery. The pharmacokinetics and dynamics of neostigmine, pyridostigmine and edrophonium will be determined in patients with normal renal function and in patients with renal and hepatic dysfunction, and correlated using a conceptual model. The relationship between antagonism of neuromuscular blockade and the inhibition of erythrocyte acetylcholinesterase will be determined as an integral part of the pharmacodynamics.